Urban title

Urban Protocol Bundle
 

urban intro

The urban environment is a reflection of urban dynamics. These dynamics include the surface and atmosphere energy balance, the transfer of air masses, the dispersion of air pollutants, and the energy/heat fluxes between the surface-atmosphere interface.

The areas within urban space are heterogeneous with respect to building and population density, land use/cover, greenery, cooling sinks, the intensity and spatial dispersion of anthropogenic heating sources, rain run-off features, and more.

urban pic

Urban Bundle



The Changing Urban Environment


Urban spaces are typically classified as areas of substantial human infrastructure and high population density. The combination of these two factors can significantly alter the local habitat's natural state and environmental cycles. Furthermore, urban environments can manifest in many different ways throughout the world depending on the available resources and culture of the people constructing it.

In recent years, however, there's been a shift in our perception of the urban environment. Today, we don't think of urban spaces as simply an agglomeration of buildings, but rather as a ‘living organism” that is constantly changing, mostly due to human intervention. With this newfound point of view, it's important to:

  1. Take note of individual and nested systems from the natural environment, the built environment, and the socio-economic environment.
  2. Define the physical, chemical, and environmental processes and interactions that influence and/or control the urban environment.

Given the many small-scale variations caused by the built environment, contributions from citizen scientists are particularly needed to adequately characterize the urban environment. Inside the Urban Bundle, you can find a collection of protocols, prompts, and projects related to these issues and their intersections with various Earth Spheres.

 



Bundle Overview
 

  • Atmosphere
    • Air Temperature
      • Concrete and buildings found in cities and towns affect how much heat is radiated away from the Earth. This irradiated heat can affect local air temperatures which have cascading effects for other parts of the environment.
    • Clouds
      • The cloud cover over a city affects the land-air energy budget through many different parameters, like surface temperature, relative humidity, and precipitation. Conversely, cities can also affect the formation of local clouds by limiting evaporation and vegetative transpiration rates. 
    • Precipitation
      • Areas covered with artificial, impervious materials like concrete or asphalt can experience higher flood risks from precipitation than more natural spaces.
    • Surface Temperature
      • Surface temperature is an important parameter for assessing the presence and intensity of the surface urban heat island. It's an essential factor for the estimation of the energy budget in an urban area because it controls the heat transfer from the ground to the air—also known as sensible heat. 
    • Relative Humidity
      • Evaporation acts as a cooling mechanism for cities. However, impervious urban materials, like asphalt and concrete, don't retain water, so evaporation rates from surface and subsurface soils are drastically limited. Lower evaporation rates also impact the overall relative humidity in an urban environment. 
  • Biosphere
    • Biometry
      • By measuring the heights of the tree and vegetation canopy in urban environments, we can better understand how variables like surface temperature, humidity, and building heating loads are affected by greater or lesser amounts of natural shade.
    • Land Cover
      • Since cities replace natural, vegetative land cover with harder surfaces, it's important to know how these changes in material affect local temperatures, albedo, emission coefficients, and the land-air energy budget. This knowledge also helps guide us on the least ecologically impactful way to expand our urban environments.
  • Hydrosphere
    • Water Temperature
      • The temperature of urban water bodies influences amount of airborne water vapor, and thus humidity, cloud cover, and precipitation. Higher temperatures typically lead to higher evaporation rates, while lower temperatures have the opposite affect.
  • Pedosphere (Soil)
    • Soil Characteristics
      • The characteristics of urban soil are greatly influenced by human activity. For example, the materials comprising the soil can change significantly from their original form after a building or road construction project begins.   
    • Soil Infiltration
      • Impervious urban materials typically have lower water infiltration rates, which can lead to higher risk of flooding after extreme precipitation events. 
    • Soil Moisture (Gravimetric)
      • Through anthropogenic changes to land cover, soil characteristics, and the atmosphere, we are directly affecting the soil moisture content in urban areas. The water content of the soil has a significant impact on the areas biome type as well as the plants/animals that can live in that area. 
    • Soil Temperature
      • By converting natural landscapes into urban ones, we affect the temperature of the soil beneath us. Changes in the soil's temperature has broad impacts on the underground ecosystem, and thus the environment on the surface.


Check out our chart below for a visual representation on how all these protocols fit together within the Urban Bundle: 
 

Urban areas comprise less than 3% of the Earth’s surface, however their proliferation has been largely driven by socio-economic factors with little consideration for their environmental impact. Today, a particularly important aspect for studies of urban environments is the lack of balance between natural and built spaces. These imbalances influence a host of other factors including, urban microclimatic changes, the depletion of green spaces, increases in anthropogenic heat sources, proliferations of impervious sources, deteriorated air quality, increase flooding and much more.

Air pollution and heat islands within urban ecosystems are especially crucial areas of study due to their negative impacts on human health. Air pollution impacts are exacerbated for members of vulnerable groups, while increased temperatures lead to more energy used for cooling. The latter can lead to poor city energy efficiency, intensified energy poverty, and greater disparities between socio-economic classes.

These two issues are mostly confined to medium- and large-size cities. However, the differences measured between urban and rural area can be quite significant. For example, air temperature measurements can raise by 6-8 degree Celsius as you move from the countryside into the built environment. Furthermore, poor urban planning can lead to temperature variations within the city itself, creating areas of excessive thermal intensity.

This intensified thermal heating is a result of the change in natural green spaces to hard environments with significant heat loads. Where forests or fields would cool the local area through evapotranspiration processes, urban settings lack the moisture to adequately cool the habitat through the same methods. Additionally, buildings have a strong impact on the flow of wind through the area and, in most cases, suppress the outgoing thermal radiation close to the ground.

To get a better idea of all the variables that comprise the Urban Bundle, check out the following case studies trying to answer the questions: 
​​​

  1. How does the thermal environment vary within a city?
  2. How do materials affect the thermal environment in cities?
     

Case 1: Define and analyze the state of the thermal environment in a city
 

An important case study is to define and analyze the state of the thermal environment in a city. This is because people who live in cities with burdened thermal environments, face increased health risks due to thermal discomfort and the increase of photochemical air pollutants, whereas they need to consume additional energy for their cooling needs. In order to achieve the objectives of this Case Study, you need to combine diverse environmental information and make use of several GLOBE Protocols.

Table 2 provides an extended list of environmental information which need to be monitored, links it to the GLOBE Protocols included in the Urban Bundle Protocol and also provides a description on the need to apply each of the GLOBE Protocols on a physical parameter basis.

Table 2. A description of the application of the Urban Bundle Protocol in view of assessing the state of the thermal environment in cities.

Thematic category

GLOBE Protocol

Why do we need the GLOBE Protocol

Atmospheric boundary layer

 

(Energy Cycle)

Atmosphere Protocol

Air temperature and surface temperature support the spatial and temporal definition of the state of thermal environment in a city.

Precipitation allows the qualitative and quantitative estimation of the evaporation intensity, the latter being a significant cooling mechanism in a city.

Clouds influence the incident solar energy to the ground; thus their presence and extent in space and time, control air and surface temperatures.

Urban expansion

Biosphere Protocols

Land cover classification allows the correlation of air and – mostly – surface temperatures to the type of materials on the ground. It is important to have a close look on this correlation by completing Table 3.

Urban hydrology

(Water Cycle)

Atmosphere protocol

 

Biosphere and Pedosphere Protocols

 

Hydrosphere Protocol

Precipitation is critical for the water cycle and the extraction of conclusions on the dryness of the soil and the amount of soil moisture.

 

Soil infiltration supports the understanding of the capacity of the ground to store water, making it available for uptake by plants and soil organisms. Low soil infiltration may result in flooding following extreme rain events.

 

Water temperature influences the local availability of water vapor as the higher the temperature, the higher the evaporation rate.

Urban soil

Pedosphere Protocols

All soil related parameters (soil characterization, soil infiltration, soil moisture, soil temperature) are important to assess energy and heat fluxes between the ground and the air above.

Urban heat island

Biosphere Protocol

Atmosphere Protocol

Hydrosphere Protocols

Land cover is important for assessing measurements of surface temperature and air temperature (see also Table 3).

 

The higher the temperature of a water body, the higher its cooling intensity.

Greenery in the city

Biosphere Protocols

 

Atmosphere Protocols

MUC and GLOBE Observer Land Cover Classification support the spatial depiction of the areas in cities. In green areas, Biometry and GLOBE Observer Tree observations help define the properties of urban vegetation.

Air temperature and surface temperature in green areas allow the extraction of information on the cooling intensity of greenery.

 

An important application is the detection of the Urban Heat Island* in cities. For this you need to collect air or surface temperatures – for different times of the day - in the city center and suburban or rural areas and define their difference in degrees Celsius. Be aware that you need to always compare the temperatures from the same areas so as to achieve the needed consistency.
 



Case 2: The impact of materials to the thermal environment in cities
 

Different city materials develop temperatures which differ even if the amount of incident radiation is the same. This is due to their properties, for instance albedo, emission coefficient, and thermal capacity. In addition, even the same material may develop different temperatures in the event of changes in incident radiation (for instance due to shading) or material degradation.

In order to examine the role of materials in shaping the thermal environment in cities, you may use a thermal radiometer to record surface temperature for different surface materials. Fill Table 3 by taking three measurements (M1, M2, M3) at the same time of the day so as to produce the average value.

*An urban heat island (UHI) is an urban area that is significantly warmer than its surrounding rural areas due to human activities. The temperature difference usually is larger at night than during the day, and is most apparent when winds are weak.

Type of material

Time of day

M1

deg Celsius

M2

deg Celsius

M3

deg Celsius

M average

deg Celsius

Cloud cover

(yes or no)

Comments

Bare soil

 

 

 

 

 

 

 

Asphalt

 

 

 

 

 

 

 

Grass

 

 

 

 

 

 

 

Wood

 

 

 

 

 

 

 

Cement

 

 

 

 

 

 

 

Car surface

 

 

 

 

 

 

 

Marble

 

 

 

 

 

 

 

Other

 

 

 

 

 

 

 

Table 3. Recording of land surface temperature per type of material (M: measurement).

Urban population worldwide has grown rapidly from 751 million in 1950 to 4.2 billion in 2018. Asia, despite its relatively lower level of urbanization, is home to 54% of the world’s urban population, followed by Europe and Africa with 13% each. Today, the most urbanized regions, with percentage of population living in urban areas, include:

  • Northern America: 82% 
  • Latin America and the Caribbean: 81%
  • Europe: 74%
  • Oceania: 68%

*Measurements from 2018

The level of urbanization in Asia is now close to 50%. In contrast, Africa remains mostly rural, with 43% of its population living in urban areas. Overall, 55% of the world’s population lives in urban areas, a proportion that is expected to increase to 68% by 2050. 

Given these increases in urbanization, it's important to ensure that the natural ecosystems in our cities are in good condition. To support this effort, you can take action by examining the state of the environment in the city where you live and try to identify the parameters that influence the quality of life for city dwellers. You can also help raise awareness of urban ecosystem problems by reporting your findings to our databases and other environmental authorities to better understand how the urban habitat affects the various Earth spheres. 

Acknowledgments

Compiled by:

  • Prof. Constantinos Cartalis
  • Dr. Dixon Butler

Many thanks to the members of the Science Working Group for their comments. 

References